Director orientation of nematic side-chain liquid crystalline polymers under shear flow: Comparison of a flow-aligning and a non-flow-aligning polysiloxane

The flow behavior and phase structure of two side-chain liquid-crystalline polysiloxanes with the same mesogens but different spacers of either four (PSi4) or six (PSi6) methylene groups are studied in the nematic phase by H-2 NMR, polarization microscopy, and scattering of light, neutrons, and X-rays. PSi4 is flow-algning, forming a monodomain with the director close to the flow direction, whereas PSi6 is non-flow-aligning showing a polydomain structure with a preferred director orientation corresponding to the log-rolling state. The flow behavior of PSi6 is related to the presence of strong smectic clusters. The director tilt in the smectic clusters of both polymers is reported.